Numerical study of ice freezing process on fin aided thermal energy storage system

Abstract

The present numerical study is based on the solidification process of water when used as a phase change material (PCM) in a latent thermal energy storage system (LHTESS). LHTESS can balance varying energy demand and supply by storing surplus energy during off-peak hours. The present study investigated a tube-in-tank storage system where the refrigerant flows inside the tube and PCM is outside the tube. Enhancement techniques like fins on the HTF tube's surface enhance the effective heat transfer rate on the PCM side. A two-dimensional transient numerical study has been carried out to optimize the number of longitudinal fins for a possible maximum decrease in solidification time, after which increasing the number of fins does not alter the rate of solidification. Moreover, a parametric study has been done to see the effect of varying temperatures of the refrigerant, tube diameter, and orientation of the HTF tubes on the phase change process. A comparison for solidifying stored PCM by applying different parametric conditions has been carried out in terms of heat transfer rate and heat transfer coefficient. Numerical results obtained indicate that 15 fins are the optimum case for achieving the balance between the solidification rate and the stored PCM mass. A maximum overall increment in the heat transfer rate is achieved around 20% more with the optimum number of fins emphasizing its vital significance over no fin case with 67.38% and 30.25% more production of ice at 500 s and 1500s, respectively. However, a least enhancement of nearly 6% is seen in the rate on changing the tube orientation from inline to staggered for given number of the tubes. In addition, a lower tube wall temperature of 257 K is found to be 89% faster than the higher temperature of 265 K in shortening the required solidification time, therefore quicker freezing of the domain is obtained.